This invention relates to an air feed tube assembly for a pneumatic chuck.
In known air feed tube assemblies, a set of coaxial air feed tubes are provided by means of which compressed air can be selectively fed from an air supply so as to open and close the gripping jaws of the pneumatic chuck. The air feed tube assembly itself is coupled to the machine spindle of a turning lathe so that the turning moment generated in the lathe is transmitted via the assembly to the pneumatic chuck. In consequence, and in addition to the pneumatic coupling of the air feed assembly with the pneumatic chuck, the chuck must also be mechanically coupled to the air feed tube assembly so as to allow for the transmission of the turning moment. This mechanical and pneumatic coupling of the air feed tube assembly to the pneumatic chuck is effected at one end of the air feed tube assembly, whilst the other end of the assembly is coupled to a rotary air feed joint which is, in its turn, coupled to the air supply. Clearly, in view of the fact that the air feed tube assembly rotates whilst the air feed joint, coupled to the fixed air supply, must of necessity be stationary, the air feed tube assembly must be coupled to the air feed joint via a suitable bearing and, in this connection, the known form of coupling has been by way of closely fitting bearing surfaces.
In many cases, it is known to provide for the flow of a liquid coolant medium through an innermost tube of the air feed tube assembly and, here again, means are provided for coupling the air feed joint to a source of liquid coolant. Where such liquid coolant is provided, it has to be ensured that the liquid coolant itself does not leak into the region of the bearing surfaces.
With known air feed tube assemblies for pneumatic chucks, the assembly is screw-coupled to the pneumatic chuck and the entire drive from the lathe is transmitted to the chuck via this screw coupling. However, such screw-coupling carries with it the danger that, each time the drive force is interrupted, reversed or reduced, a reverse turning moment acts upon the air feed tube assembly which tends to result in the uncoupling of the assembly from the chuck.